This invention is directed to a light guide, and in particular to a light guide for transmitting large quantities of light energy from one place to another.
As exemplified by U.S. Pat. No. 247,229, which issued to W. Wheeler on Sept. 20, 1881, the illumination of entire buildings by a central lighting system has long been desired because of its many advantages. For example, the piping of light from a central source brings about efficiency due to the source size, and such a source may include the direct use of sun light. In addition, a central lighting system would provide cool light at its outlets with the heat being expended at the source.
Presently, there are two basic methods of guiding light energy. The first method, exemplified by U.S. Pat. No. 2,362,175 which issued to H. Swanson on Nov. 7, 1944, is to employ a dielectric waveguide, which is a solid rod made of transparent material. The light rays are reflected inward by the surface of the rod in a process known as total internal reflection. This process is nearly 100% efficient in containing the light, but unfortunately all reasonably priced transparent materials actually absorb most of the light in relatively short distances, i.e. within a few centimeters to a few meters. The method is therefore used mainly in optical communications systems, where small quantities of extremely expensive dielectric material are used.
The second technique is to have the light propogate mainly through air, and to periodically redirect the light to keep it confined and travelling in the correct direction. Until now there have been three methods of accomplishing this redirection. A first method, as exemplified by U.S. Pat. No. 3,506,331 which issued to R. Kompfner on Apr. 14, 1970, is to use focussing lenses or mirrors at intervals down a hollow pipe. In a second method, a hollow pipe with a mirrored inner surface is used to keep the light travelling down the pipe, such a pipe is shown in U.S. Pat. No. 3,700,900 which issued to J. A. Herleikson on Oct. 22, 1972. In a third method which is illustrated in U.S. Pat. No. 3,583,786 issued to E. A. J. Marcatili on June 8, 1971, the pipe consists of an inner cylinder, usually air, surrounded by pairs of dielectric layers wherein the losses are purported to decrease with the number of pairs of layers.